Traditional printed circuit boards (PCBs), populated with electronic components, are usually disposed of at the end of their useful life either by incineration or as landfill. This can give rise to undesirable pollutants, increasing volumes of non-biodegradable waste products, and wasting of materials and components which could in theory be reused.
European Waste Electrical and Electronic Equipment (WEEE) legislation is likely to require that up to 70% of electronic equipment waste is recycled. Currently, over 100 million electrical units are discarded annually in the UK, with 85% of this waste going to landfill and the remainder being sent to furnaces in order to reclaim precious metals.
There is therefore a desire to provide a technology which enables easy reuse and/or recycling of electronic circuits and components, both to meet the requirements of legislation and to benefit from the economic advantages of recovery of expensive components and reusable materials.
The present invention provides an electronic circuit assembly which utilises particular adhesives in the construction of the assembly and the attachment of components to a substrate, which allow for the disassembly of the structure, and the separation and recovery of constituent parts and components for recycling or reuse. In particular, the adhesives are designed to be releasable (or ‘unzippable’) under certain conditions (e.g. heating and/or exposure to water at elevated temperature range), to allow for disassembly under these conditions, which enables straightforward disassembly of the circuit components whilst allowing the circuit to function normally in conventional operating conditions. This leads to very high percentage recovery levels and recyclability above 90% achieved. Electrically conductive and non-conductive adhesives can be used in different parts of the assembly, as appropriate, to provide the required structural and/or electrical connections, while still enabling the assembly to be separated out easily into its constituent parts as required. Using the technique and adhesives described below, it has been found that the adhesives themselves are recoverable, such it is possible to separate the adhesives from the circuit components and substrate(s) for reuse or disposal of the individual constituents of the assembly, in a way which is not possible with soldered components, since solder cannot be recovered in a way which allows for reuse of the substrate.
Conventional electronic circuits have traditionally utilised solders for the attachment and electrical connection of components. Reworking of solder connections is possible, for example for the replacement of failed components, but this is impractical and inefficient as a way of recovering circuit components for reuse. Adhesives have been known to be used in the manufacture of electronic circuits, but this is typically for the purpose of locating components in position, while electrical connections are made using conventional soldering techniques. For example, U.S. Pat. No. 4,215,025 A discloses the use of a water soluble polymeric compound to keep components in place on a printed circuit board during soldering operations, after which the compound is completely removed using a water rinse, leaving a conventionally soldered circuit board.